1. Field of the Invention
The present invention relates to a field emission cathode (FEC) type electron gun.
2. Description of the Related Art
In a first type of conventional FEC type electron gun, a cold cathode is constructed of one substrate (cathode electrode), one gate electrode, an insulating layer therebetween, and a plurality of cone-shaped emitters formed within openings perforated in the gate electrode and the insulating layer. If a high voltage is applied between the gate electrode and the cone-shaped emitters, a strong electric field is generated around the tips of the cone-shaped emitters, so that electrons are emitted therefrom. (see: C. A. Spindt, "A Thin-Film Field-Emission Cathode", Journal of Applied Physics, Vol. 39, No. 7, pp. 3504-3505, June 1968). This will be explained later in detail.
The above-described FEC type electron gun has an advantage in that a high density of current is realized and the velocity of dispersion of emitted electrons is small as compared with a conventional thermionic cathode electron gun.
Also, in order to effectively converge an electron beam emitted from the electron gun, focusing electrodes are provided (see: JP-A-5-343000 and JP-A-7-235258). This will also be explained later in detail.
In a second type of conventional FEC type electron gun, in order to obtain a stable electron beam, a field effect transistor (FET) is incorporated as a constant current source into the same substrate as the cold cathode (see: JP-A-8-87957). This will also explained later in detail.
In a third type of conventional FEC type electron gun, the driving system of the second type of FEC type electron gun is applied to a plurality of cold cathode elements. This will also be explained later in detail.
In the third FEC type electron gun, however, since all the cold cathode elements are controlled by a single FET, each of the emission currents of the cold cathode elements fluctuates, and as a result, the distribution of current density within the entire cold cathode is fluctuates with time, and thus, a stable electron beam cannot be obtained.